The present invention relates to ovens and more particularly to an oven for processing coated wire to evaporate and cure the solvents and other volatile components present in the coating material.
Wire for many electrical applications is generally coated with a thin film of insulating material such as oleoresinous enamel. The coating material is dissolved or suspended in a liquid solvent or carrier and the wire is dipped into this bath to obtain an even coating. Consequently, a wet film is present on the wire which thereafter is passed through an oven to evaporate the solvent or carrier and to cure the remaining solid coating material.
It has been known for some time that separate control of the evaporation and curing processes is required to obtain wire at a high processing volume with good results. To this end the prior art ovens provide separate evaporating and curing zones, the wire first passing through the evaporating zone and heated by gas enter adjacent the wire inlet, and then through the curing zone and heated by gas entering adjacent the wire outlet the gas exiting the work chamber through a common outlet between the zones. Since obnoxious, if not noxious, vapor and fume from the solvent are released by the process, the gases leaving the zones are recirculated and routed to a catalytic burner or to a high temperature burner for a sufficient period of time to oxidize the volatile vapors and fumes. Ovens utilizing the catalytic oxidizer are illustrated in U.S. Pat. Nos. 3,351,329 (Thomas); 3,183,605 (Argue et al); 3,183,604 (Stauffer); 3,106,386 (Harris); 2,921,778 (Ruff) and 3,265,033 (Touze et al). An example of an oven constructed with a non-catalytic oxidizer is illustrated in Dumas U.S. Pat. No. 3,810,736.
The constructions of these prior art ovens, however, have a number of limitations. For example, the known ovens have been constructed as integral units, i.e. the framework, wall structures, door closures, partitions and ducting etc. have been built, and welded together as a unit. Thus, large amounts of heat are transferred from the hot internal sections to the outer skin. Over a period of time as expansion and contraction of the hot sections occur large amounts of distortion resulting in failure of certain of the elements have required the rebuilding of the entire oven.
Another and related deficiency of the prior art ovens is a lack of flexibility to accommodate wires of largely varying sizes. The wires move through a passageway or work chamber confined between fixed structural members. Generally, the work chamber can accommodate a range of wire sizes, but the range is limited. Thus, if a wire of a greatly different size is to be processed either a new oven is required or the existing oven must be disassembled and rebuilt to the new size range.
A further limitation of the ovens in the prior art is their inability to process different size or differently coated wires simultaneously. The optimum temperature profile through the evaporation and curing zones varies with wire size and coating types so that the simultaneous processing of more than one size or coating type is not practicable with the known ovens of the prior art.